This project examines the risk for MDD in breast cancer (BC) patients. The overarching hypothesis is that although distress highly prevalent, risk for MDD is moderate and predictable past history of MDD in combination with current distress, but is largely treated inadequately. The first aim is to assess the prevalence, nature, course, and co-morbidity of psychological distress and MDD at entry into cancer and across treatment. The second aim is to test rival hypotheses regarding risk for MDD over the course of the cancer experience with reference to psychological distress and past history of MDD. The third specific aim is to examine the extent, correlates, and outcome of clinician detection and intervention for MDD in routine cancer care. The fourth specific aim is to examine the effects of inclusive, exclusive, and substitutive diagnostic strategies on the nature and prevalence of diagnosed MDD. The project involves multi-stage screening/clinical interviewing for new BC patients, and selection of a stratified sample on the basis of psychological distress, current MDD, and history of MDD. Five groups of women will be followed over this 12-month longitudinal study. One group will consist of women with current MDD. The other groups will consist of nondepressed women nested within a 2 (distressed/nondistressed) x 2 (history/no-history of depression) design. Relevant variables will be assessed via self-report and interview, and chart abstractions will assess staging of BC and current medical and psychiatric treatments. Cancer clinicians will rate the women for distress, depression, functional status and suitability for treatment. Women will be reassessed at 3, 6, 9, and 12 months. This project has important clinical, mental health services, public policy implications. It will provide data essential to establishing the mental health needs of BC patients and the rational design of services to meet these needs. It will allow the design of algorithms for the prevention, detection, and treatment of MDD. Results will also have implications for the training of oncologists, as well as mental health and primary care clinicians who provide the bulk of mental health services to patients and survivors outside the cancer setting.